A conventional way of mounting a sight on a gun is to provide an upper surface of the gun with a transverse groove of dovetail cross section into which a correspondingly shaped dovetail projection of the sight assembly is slidably insertable to attach the sight to the gun. The dovetail projection is a tight friction fit in the groove to form a rigid connection between the parts, and is an integral portion of an element which projects upwardly beyond the groove and carries the sight at the top of the gun, Installation of the sight on a gun requires precise filing or machining of the dovetail projection by an expert gunsmith in order to attain the desired rigid connection capable of withstanding the forces encountered in handling and firing of the gun. The gunsmith must carefully remove material from the undersurface of the dovetail projection until that projection has exactly the right degree of friction fit within the mating dovetail groove in the gun. The projection is then driven into the dovetail groove to mount the sight rigidly to the gun.